/Engine/Source/Runtime/Engine/Classes/Kismet/BlueprintPathsLibrary.h
Changes the extension of the given filename (does nothing if the file has no extension)
static [FString](API\Runtime\Core\Containers\FString) ChangeExtension ( const [FString](API\Runtime\Core\Containers\FString) & InPath, const [FString](API\Runtime\Core\Containers\FString) & InNewExtension )